A column of armored vehicles flying Russian flags drove into a Ukrainian city controlled by pro-Russia insurgents Wednesday, dampening the central government’s hopes of re-establishing control over restive eastern Ukraine.

Still, it was far from clear just who these mostly masked men were and what their presence meant for eastern Ukraine, which has seen a surge of support for closer ties with Russia and against the new government in Kiev, which wants closer links to Europe.

The six vehicles with troops in camouflage sitting atop entered the city of Slovyansk, a hotbed of unrest against Ukraine’s interim government. Insurgents in Slovyansk have seized the local police headquarters and the administration building, demanding broader autonomy for their eastern Ukraine region and closer ties with Russia. Their actions have been repeated in at least eight other cities in eastern Ukraine.

One of the men said they were Ukrainian soldiers who had defected to the pro-Russian side — which raises the specter of an uprising by defected Ukrainian forces in Ukraine’s eastern regions.

But an AP journalist overheard another soldier suggesting that the handover of the vehicles took place under duress.

“How was I supposed to behave if I had I had guns pointed at me?” the soldier, who did not identify himself, said to another resident.

Further adding to the confusion, a senior Ukrainian lawmaker denied that any defections had taken place and instead insisted the men on the vehicles were Ukrainian soldiers using a false flag to move about freely.

The uniform worn by some of the men on the vehicles was different from that of the gunmen on the ground, many of whom had pro-Russian ribbons attached to their shoulders.

Eastern Ukraine was the support base for ousted President Viktor Yanukovych, who fled to Russia after months of protests over his decision to back away from closer relations with the European Union and turn toward Russia. Opponents of the government that replaced him allege the new authorities will repress eastern Ukraine’s large Russian-speaking population — events which the U.N.’s human rights body says has not happened.

Reflecting the West’s concern, German Chancellor Angela Merkel called Russian President Vladimir Putin late Tuesday to discuss the situation in Ukraine and preparations for diplomatic talks in Geneva on Thursday.

The Kremlin said Putin told Merkel that “the sharp escalation of the conflict places the country in effect on the verge of a civil war.” Merkel’s office said she and Putin had “different assessments” of the events in Ukraine.

In Brussels, NATO announced it was immediately strengthening its military footprint along its eastern border — which often borders Russia — in response to Russia’s aggression in Ukraine.